Fields outside Benambra, Victoria, Australiasuffering from drought conditions. A drought is an extended period of months or years when a region notes a deficiency in its water supply whether surface or underground water. Generally, this occurs when a region receives consistently below average precipitation. It can have a substantial impact on the ecosystem andagriculture of the affected region. Although droughts can persist for several years, even a short, intense drought can cause significant damageand harm the local economy.
Succulent plants are well-adapted to survive long periods of drought. Many plant species, such as cacti, have adaptations such as reduced leaf area and waxy cuticles to enhance their ability to tolerate drought. Some others survive dry periods as buried seeds. Semi-permament drought produces arid biomes such as deserts and grasslands.  Most arid ecosystems have inherently low productivity. This global phenomenon has a widespread impact on agriculture. Lengthy periods of drought have long been a key trigger for mass migration and played a key role in a number of ongoing migrations and other humanitarian crises in the Horn of Africa and the Sahel. Consequences
Dry earth in the Sonoran desert, Mexico.
Periods of drought can have significant environmental, agricultural, health, economic and social consequences. The effect varies according to vulnerability. For example, subsistence farmers are more likely to migrate during drought because they do not have alternative food sources. Areas with populations that depend on as a major food source are more vulnerable to drought-triggered famine. Drought can also reduce water quality, because lower water flows reduce dilution of pollutants and increase contamination of remaining water sources. Common consequences of drought include: Common consequences of drought include:
Diminished crop growth or yield productions and carrying capacity for livestock Drought can also reduce water quality, because lower water flows reduce dilution of pollutants and increase contamination of remaining water sources. Dust bowls, themselves a sign of erosion, which further erode the landscape Dust storms, when drought hits an area suffering from desertification and erosion Famine due to lack of water for irrigation
Habitat damage, affecting both terrestrial and aquatic wildlife Malnutrition, dehydration and related diseases
Mass migration, resulting in internal displacement and international refugees Reduced electricity production due to reduced water flow through hydroelectric dams Shortages of water for industrial users
Snake migration and increases in snakebites
War over natural resources, including water and food
Wildfires, such as Australian bushfires, are more common during times of drought. Globally
Drought is a normal, recurring feature of the climate in most parts of the world. It is among the earliest documented climatic events, present in the Epic of Gilgamesh and tied to the biblical story of Joseph's arrival in and the later Exodus from Ancient Egypt. Hunter-gatherer migrations in 9,500 BC Chile have been linked to the phenomenon, as has the exodus of early humans out of Africa and into the rest of the world around 135,000 years ago. Modern peoples can effectively mitigate much of the impact of drought through irrigation and crop rotation. Failure to develop adequate drought mitigation strategies carries a grave human cost in the modern era, exacerbated by ever-increasing population densities. Regions
Lake Chad in a 2001 satellite image, with the actual lake in blue. The lake has shrunk by 95% since the 1960s.
Sheep on a drought affected paddock near Uranquinty, New South Wales. Recurring droughts leading to desertification in the Horn of Africa have created grave ecological catastrophes, prompting massive food shortages, still recurring. To the...
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